Invasive Species and Historic Extinctions

There are now believed to be between 5,000 and 180,000 Burmese Pythons (Python molurus bivittatus) living in the Florida Everglades. These, it is assumed, are the progeny of a few released and escaped pets. There are also multitudinous Green Anacondas, Yellow Anacondas, Asiatic Reticulated Pythons, South African Pythons and boa constrictors. Some of these grow beyond 20 feet and 200 lbs in weight. They are the snakes that entwine and crush their prey, before swallowing it whole. They are all introduced species; none of them are natural to Florida.

"Oh dear," one might say, "I do hope they don't eat people."

Well, they do actually, though seldom. They eat anything they can find in the wild, including birds. Of those pythons that have been caught and examined, 80 per cent were found to have eaten birds, and that is one major problem.

The wildlife species of Florida are not genetically prepared to avoid such exotic snakes, so have few defenses against them. Herons, ibis, storks and even small wrens have been found in the snakes' digestive tracts.

It is clear that having 10,000 exotic pythons living in the Everglades is not as it should be. If Burmese Pythons were a travelling species, one that is destined to move about the Earth, they would either have wings, or spend many thousands of years accomplishing their spread. This transfusion of exotic snakes to Florida was accomplished, not by natural means, but by humans. A 2011 study released by the University of Florida states that between the first release of a non-native species in 1863 - the greenhouse frog from the West Indies - and the year 2000, there have been 137 exotic and invasive reptile and amphibian species released into the Florida wilds.

Some young couple with a love of reptiles, and a pet Burmese Python named Cedric who had grown to fifteen feet long, was surely being kind when they released him into a local body of water.

"Cedric you'll be happy here in this nice warm water. You can live out your days in peace and freedom, and we are so sorry we can't take you to New York with us, but you wouldn't be happy in a little apartment. Bye-bye Cedric and good hunting."

Well, not only did Cedric enjoy good hunting, he also enjoyed meeting saucy Cynthia, a sultry and bonny serpent, also born in Burma. She too had become far bigger than that slithery little 40-inch snake she had been when first adopted, and, like Cyril, she also had been slipped into the waterways of Florida. We can imagine, when she first realized she was no longer alone, with what ardor the sexy Cynthia fluttered her lovely eyes at poor sensitive Cyril. Cyril stood no chance. Oh the conjugal ecstasy! Oh the joinings and the squeezings! Oh such pythonic fecundity! And oh what a big family they raised! Then, once their offspring got together with the other released serpents, how the waters of the everglades boiled with ever more ritual entwinings. Those female snakes can release up to a hundred eggs at a time. So Cynthia, with Cedric as her mate, could easily have produced thousands of offspring in just her lifetime.

None of those fine nature-loving and snake-releasing human couples thought they were helping to establish dynasties of untold thousands of pythons - pythons that would work very hard to de-populate the birds and animals of Florida.

In January 2012 a US study revealed that between 2003 and 2011 many southern Florida wild animals had seen troubling decreases in their numbers. Raccoon numbers were down 99.3 per cent, opossums down 98.9 per cent, white-tailed deer 94.1 per cent, bobcats 87.5 per cent and rabbits seem to have gone completely. In that same time frame, the number of pythons caught and removed from the Everglades had risen from 50 in 2003, to about 400 in 2011. It is possible that the decline in bobcats and foxes could be due, in part, to the disappearance of their prey animals, leading to starvation.

With the nest-raiding and egg-enjoying raccoons gone, the birds may be free of one predator, but they now have to learn to deal with another.

On the island of Guam, Brown Tree-snakes were accidentally introduced from New Guinea either during, or just after, the Second World War. Within forty years Guam had lost all breeding colonies of sea birds. Ten of the thirteen forest bird species had become extinct, including five endemic to that island. Also extinct were six of the ten lizard species and two of the three bat species. Amongst the forest birds lost for all time are the Guam Flycatcher, the scarlet and black/brown winged Cardinal Honeyeater, the Rufous Fantail, the White-throated Ground Dove and the Bridled White-eye. Two species still exist in captive breeding programs. They are the turquoise-grey and russet-breasted Micronesian Kingfisher and the very handsome Guam Rail.

It is believed that the Brown Tree-snakes first stowed in packing cases when the US navy was leaving New Guinea and establishing a base on Guam during or after the Second World War. They were first noted in the 1950s and became more abundant by 1960. By 1965 they had colonized the central part, or half, of the island and by 1968 had reached all parts of the island. By 1984 the Guam wildlife extinctions were complete, although there are a few other species that are managing to survive on the brink, so to speak. There are now estimated to be 13,000 snakes per square mile, which is possibly the highest density of snakes in the world. Now that the native mammals and birds have been so massively reduced we have to hope the near future will bring a mass starvation die-off of the snakes.

Since the colonization of Guam, Brown Tree-snakes have been carried by military aircraft from Guam to the Marshall Islands, Diego Garcia, Honolulu, Oahu, Okinawa, Saipan, Wake Island, Taiwan, Darwin, Australia, Spain, Corpus Christi, Texas and other places. In Corpus Christi the snake had spent 7 months in a packing case of household goods before it was found. They frequently seem to travel in the landing gear of US military planes. One snake was found in Singapore aboard a navy plane that had only stopped long enough to refuel on Guam.

Among other species that have had similar impacts on the native birds and reptiles can be included rats, cats, dogs, goats, and free foraging domestic pigs. When these animals were accidentally left on islands, with few or no predators, they very quickly killed off most of the ground nesting birds, and the tree nesting ones as well.

An example of the damage that introduced insects can inflict is found with the Asian Long-horned Beetle (Anoplophora glabripennis). This is a large 1-1.5 inch (2.5-4 cm) black beetle with white spots and with very long horn-like antennae. Its natural home is in far eastern Asia (China, Korea and Japan) where it goes under the delightful name of the Starry Sky Beetle, or sometimes the Sky Beetle. It was first noted in 1996 in eastern USA and Canada, though it probably arrived aboard packing cases sometime in the 1980s. A study published in the Canadian Forestry Journal in August in 2011, noted that the destructive beetle shows a very real liking for maple trees, especially the sugar and red maples - those magnificent trees that supply the wonderful yellow, orange and red fall colours in Quebec and New England. They also supply the maple syrup that we humans enjoy on our pancakes. These maple forests have important economic benefits to the regions where they grow in terms of tourism, maple syrup harvesting and furniture grade hardwood. In 2011 the beetle was very well established in the maple forests surrounding Worcester, Massachusetts and was spreading.

I'm sure few people would deny a beetle a meal. After all, every country is home to many species of beetles that go about their business daily and unnoted. The trouble is that the grubs or larvae of this particular invader eat for 10 to 22 months. What they eat is the sap-rich area of trees called the phloem and cambium layers. These layers, between the bark and the new wood, are rich in sugars and are the growth mechanism of the tree. If the beetles worked horizontally, all the way around the tree, they could cut off the flow of the sap causing the tree to die. After they have munched their way up, down or around the tree they make their way into the heartwood where they pupate. After the pupa stage the adult emerges from the tree through a ½-¾ inch (10-15 mm) hole. These large holes open the tree to disease, and create weakness and the potential for wind damage. It also doesn't do much for the value of the furniture wood when it is found to be full of holes. Already, in Massachusetts, 29,000 trees have been removed in one area while another 20,000 have been identified as affected. The cities of New York, Boston, Chicago and Toronto have all begun measures to beat the scourge. Whether it is possible to eradicate an invader of this type is an open question. If we use pesticides they are likely to kill as many grub-eating birds as the grubs themselves. It is lucky that the beetle usually lays her eggs, all 35-90 of them, under the bark on the same tree in which she was born. It is only after the tree is overpopulated with beetles and their larvae that the Asian Long-horned Beetles leave the tree in search of a new home. Fortunately they only fly relatively short distances. A typical flight is about 400 yards/meters, and they seldom colonize a tree further than 1 mile away from the old host tree. This potentially makes control somewhat easier than with beetles or moths that fly greater distances. They usually take up to 3 years to reach the adult stage – to become beetles – but then only live for 50–60 days, during which time they mate and produce another generation of 35-90 eggs.

We also need to consider the oceans in this context. According to the US's National Oceanic and Atmospheric Administration, the lionfish, (Pterois miles and P. volitans), which hails from the Indo-Pacific Ocean, was in 2012 becoming a menace on the Atlantic Seaboards of North and South America and the Gulf of Mexico. Lionfish are multi-striped, multihued, and multi-appendaged strange looking things. Maybe this is what gives them their charisma. People buy them for their aquariums and then, of course, release them into the sea when they grow too large. They are well-armed carnivores with few predators in the Atlantic. They feed on crustaceans and the young of any manner of fish that we also like to eat. We have no way of removing them from the ocean, and the fear is that, in the future, they will negatively affect the commercial fishing industry. In 25 years they have spread and multiplied to such an extent that in some places there are now a thousand lionfish per acre of sea.

The above species can be described as accidental introductions; however there are plenty of planned introductions most of which turned out to have terrible consequences. In fact, we humans have done some pretty stupid things over the years. Typically, we move into a pristine environment that we decide will be a great place to introduce some useful crop. We do just that, but then find that the local wildlife thrive on this new food supply. We then bring in a second alien species to defend the first by eating the native. Then we discover that the second introduction is a bigger problem than the first. This applies to the Cane Toad (Bufondae rhinella marina) in Australia.

Australia was thought to be a great place to grow sugar cane - lots of Aussie sunshine, good agricultural land and great prospects for making money. But a problem arose. The grubs of the native Greyback and French's Cane Beetles thrive on sugar cane roots. They were stunting the plants and causing a loss of both sugar production and profits. What to do? What to do?

The Bureau of Sugar Experimental Stations came up with the solution: import American Cane Toads. In 1935 the Australians imported a hundred toads from Hawaii. Those original hundred quickly bred to the 3000 that were released into the cane. Now cane toads are not only poisonous to most potential Australian predators, the females also lay between 8,000 and 35,000 eggs twice a year. So in a year a single female may produce 70,000 offspring. Granted, only about 5 per cent of those will reach maturity, but that is still 3,500. A bit of quick math will show us that 3,500 young, each producing 3,500 young annually, will give us a plague of toads in a very few years.

One problem is that these amphibians are not the jolly little fun lovers like Mr. Toad of Toad Hall and Wind-in-the-Willows renown. These are serious American troublemakers. The largest females grow to 9½ inches (24 cm) long and weigh 3 lbs (1.3 kg). Not only are they poisonous to nearly all predators that could have kept them in check, they are also very tough. They survive temperatures from 5 degrees to forty and can live in most climates although they need slow-moving or still water to breed. Anything that attacks the plump and ugly warty things usually dies. Apart from dogs and other pets, the victims include Dingo, Quoll, Freshwater Crocodile, Death Adder, Red-bellied Black Snake, Tiger Snake and Goannas. They are changing the wildlife balance in Australia.

Their advance across the eastern and northern parts of the continent has been like a flood of polluted water after a tailings pond breaks its banks. At the very beginning, in 1935 and 1936, a number of scientists and others protested the releasing of cane toads into the wild. Nonetheless, they were ignored, and now none of the early supporters of the project are around to be admonished with a cry of, "We told you so."

Another successful immigrant is the Wild Boar (Sus scrofa). It is an animal whose home range is Asia and Europe where its natural predators were tigers, leopards and wolves. Whether in the past they ever achieved a balance in the wild I don't know. There appears little chance of a balance now though, as we have killed off most of the predators. Boars have been introduced to many countries as sport for huntsmen. The countries include Australia, New Zealand, New Guinea, Uruguay, Brazil and the USA. They have been reintroduced to the UK. In England, a few hundred range in Kent, Sussex and Dorset. Since 2005, about 100 are thought to live in the areas around Dartmoor. The numbers in the USA are reckoned to be above 4 million. They cause property damage of about $800 million per year.

They are very successful animals wherever they live. The piglets reach sexual maturity at the age of twenty months, and the sows have litters of as many as ten piglets two times a year. Some other animal species, with plenty of offspring, lose a good percentage through predation. Sows, though, are very protective and vicious, so few young are killed and the numbers of animals in a group or 'sounder' can increase quite rapidly. They are opportunistic foragers and will happily consume reptiles, eggs, ground nestlings and, in Australia, lambs and young deer. A typical size of a male boar is 110 - 200 lbs (50-90 kg), though some have been recorded at over 700 lbs in Russia. A 550 lb monster was shot in a forest in France in 1999. Once established, they prove very difficult to eradicate by hunting. To introduce such animals to New Guinea, where they have no predators and will consume the ground-dwelling birds, is pure madness. It is worth remembering though, that they were made extinct in the British Isles in the 13th century, and the last boar shot in Denmark was in the early part of the 19th century. So with determination they can be removed.

These few exotic introductions illustrate, in a tiny way, the damage that we cause to the planet we call Earth and home. We unintentionally enable negative changes to the ecosystems that are just about impossible to reverse. I very much regret, though, that following in this book are tales of intentional actions that are far worse and a great deal more harmful. However, I give the assurance that I'm not only concerned to list the problems, as that would be a touch negative. Toward the end of this book things do improve, and in the final chapter, which I title "The Better Life", I suggest some changes to our lifestyle that might go some way to healing our home. Those changes won't remove the exotics, but they should result in improvements in other areas.